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Thread: Calling external programs via QProcess on Mac OS

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  1. 1st December 2014, 19:45 #1
    berliner
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    Default Re: Calling external programs via QProcess on Mac OS

    I'm pulling this up, because I found another possible way of dealing with that problem. That "solution" would use the ability of app bundles to run binaries that exist witih the bundle.

    If my app bundle contains...

    ./Foo.app/Contents/MacOS/foo
    ./Foo.app/Contents/MacOS/bar

    ...then the Foo.app can call the bar executable.

    But I want to execute something outside i.e. ghostscript. So I created a symbolic link:
    ln -s /usr/local/bin/gs ./Foo.app/Contents/MacOS/gs

    Now Foo.app can execute gs without problem. As far as I can rely on /usr/local/bin/ to be the standard location, I can even distribute Foo.app with the symbolic link itside. If not, I would need some kind of installation step that involves creating the symbolic link. The question now is, if that is kind of acceptable as solution?

    (and I still don't understand why Apple decided to implement that annoying limitation)

    The weird thing is that the problem is almost unknown in Google. Seems as if Mac applications never have to call anything outside the bundle, which is kind of unlikely.
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  2. 3rd December 2014, 06:40 #2
    jefftee
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    Default Re: Calling external programs via QProcess on Mac OS

    I use QProcess on the Mac to run ffprobe and ffmpeg successfully. All it took was to ensure that the PATH environmental variable contained the path for ffprobe and ffmpeg. Here's the code I use to prepend the PATH with /opt/local/bin, /usr/local/bin, and $HOME/bin, etc.

    Qt Code: 
    1. QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
    2. QStringList envlist = env.toStringList();
    3. envlist.replaceInStrings(QRegularExpression("^(?i)PATH=(.*)"), "PATH=/opt/local/bin:/usr/local/bin:$HOME/bin:\\1");
    4. QProcess ffprobe;
    5. ffprobe.setEnvironment(envlist);
    To copy to clipboard, switch view to plain text mode 

    Hope that helps.

    Jeff
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  3. 6th December 2014, 21:12 #3
    berliner
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    Default Re: Calling external programs via QProcess on Mac OS

    Yes, I had that idea. I modify the PATH, I print it to confirm that it really got modifie, but it's still not working.

    process.waitForStarted() just returns false and process.error() reports 0.

    Did your case really work for an application bundle? It works for me too when I directly start the binary that resides inside the bundle. Thene the program seems to get the regular execution environment. But I want to deliver an application bundle, because it makes it easier to include the Qt libraries.

    Meanwhile I created something in between. I used macdeployqt to create the bundle with all dependencies. Then I changed the bundles name and created a symbolic link in the top directory of the bundle that points to the binary under MacOS. The structure is then like this

    /Foo.app/Contents/MacOS/foo
    /Foo.app/foo -> Contents/MacOS/foo

    Now the user can run the program without traversing down the directory structure. But I still don't like it.
    Last edited by berliner; 6th December 2014 at 21:18.
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  4. 7th December 2014, 03:30 #4
    jefftee
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    Default Re: Calling external programs via QProcess on Mac OS

    Since you ran macdeployqt against your bundle, it should have copied all of the Qt frameworks into your Foo.app/Contents/Frameworks directory. My guess is that the Qt framework libraries are not able to be located when you try to start the process.

    Can you cd to your app bundle as follows and show output from otool?

    Qt Code: 
    1. cd /Applications/Foo.app/Contents/MacOS
    2. otool -L foo
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    The commands above will show the library dependencies for your foo executable. Additionally, if you'll run the following, it will display the rpath(s) in your executed with the section identified by "LC_RPATH". First command switch was an uppercase "L", the one below is a lowercase "l":

    Qt Code: 
    1. otool -l foo
    To copy to clipboard, switch view to plain text mode 

    Thanks,

    Jeff
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  5. 7th December 2014, 20:45 #5
    berliner
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    Default Re: Calling external programs via QProcess on Mac OS

    Thanks for your efforts. Here is the output from otool.

    otool -L

    Qt Code: 
    1. @loader_path/../Frameworks/QtWidgets.framework/Versions/5/QtWidgets (compatibility version 5.3.0, current version 5.3.1)
    2. @loader_path/../Frameworks/QtGui.framework/Versions/5/QtGui (compatibility version 5.3.0, current version 5.3.1)
    3. @loader_path/../Frameworks/QtCore.framework/Versions/5/QtCore (compatibility version 5.3.0, current version 5.3.1)
    4. /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0)
    5. /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0)
    6. /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 56.0.0)
    7. /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 169.3.0)
    To copy to clipboard, switch view to plain text mode 

    otool -l

    (but, actually, there is not LC_RPATH section)

    Qt Code: 
    1. Load command 0
    2.       cmd LC_SEGMENT_64
    3.   cmdsize 72
    4.   segname __PAGEZERO
    5.    vmaddr 0x0000000000000000
    6.    vmsize 0x0000000100000000
    7.   fileoff 0
    8.  filesize 0
    9.   maxprot 0x00000000
    10.  initprot 0x00000000
    11.    nsects 0
    12.     flags 0x0
    13. Load command 1
    14.       cmd LC_SEGMENT_64
    15.   cmdsize 712
    16.   segname __TEXT
    17.    vmaddr 0x0000000100000000
    18.    vmsize 0x00000000001ed000
    19.   fileoff 0
    20.  filesize 2019328
    21.   maxprot 0x00000007
    22.  initprot 0x00000005
    23.    nsects 8
    24.     flags 0x0
    25. Section
    26.   sectname __text
    27.    segname __TEXT
    28.       addr 0x0000000100002690
    29.       size 0x000000000016196a
    30.     offset 9872
    31.      align 2^4 (16)
    32.     reloff 0
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    35.  reserved1 0
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    37. Section
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    39.    segname __TEXT
    40.       addr 0x0000000100163ffa
    41.       size 0x00000000000015de
    42.     offset 1458170
    43.      align 2^1 (2)
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    90.     offset 1827496
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    121. Load command 2
    122.       cmd LC_SEGMENT_64
    123.   cmdsize 792
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    125.    vmaddr 0x00000001001ed000
    126.    vmsize 0x0000000000198000
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    137.       size 0x0000000000000028
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    329.       cmdsize 88
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    333. compatibility version 5.3.0
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    340. compatibility version 5.3.0
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    342.           cmd LC_LOAD_DYLIB
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    347. compatibility version 1.0.0
    348. Load command 15
    349.           cmd LC_LOAD_DYLIB
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    To copy to clipboard, switch view to plain text mode 
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  6. 9th December 2014, 06:08 #6
    jefftee
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    Default Re: Calling external programs via QProcess on Mac OS

    I am not entirely sure this will help, but when macdeployqt is run on my system, my binary in the app bundle winds up with the Qt libraries specified as:

    Qt Code: 
    1. @rpath/Sparkle.framework/Versions/A/Sparkle (compatibility version 1.6.0, current version 1.8.0)
    2. /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit (compatibility version 45.0.0, current version 1265.21.0)
    3. @executable_path/../Frameworks/QtWidgets.framework/Versions/5/QtWidgets (compatibility version 5.3.0, current version 5.3.2)
    4. @executable_path/../Frameworks/QtGui.framework/Versions/5/QtGui (compatibility version 5.3.0, current version 5.3.2)
    5. @executable_path/../Frameworks/QtCore.framework/Versions/5/QtCore (compatibility version 5.3.0, current version 5.3.2)
    6. @executable_path/../Frameworks/QtConcurrent.framework/Versions/5/QtConcurrent (compatibility version 5.3.0, current version 5.3.2)
    7. @executable_path/../Frameworks/QtNetwork.framework/Versions/5/QtNetwork (compatibility version 5.3.0, current version 5.3.2)
    8. /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0)
    9. /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0)
    10. /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.0.0)
    11. /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1197.1.1)
    12. /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 855.17.0)
    13. /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 1056.16.0)
    14. /usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)
    To copy to clipboard, switch view to plain text mode 

    Can you try using the following linker flags and see if the behavior works for you?

    Qt Code: 
    1. QMAKE_LFLAGS += -Wl,-install_name,@executable_path/../Frameworks
    To copy to clipboard, switch view to plain text mode 

    Not sure it will help your situation, but I've never used @loader_path, so might be worth a shot...

    Regards,

    Jeff
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  7. 11th December 2014, 00:44 #7
    berliner
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    Default Re: Calling external programs via QProcess on Mac OS

    I just installed Qt 5.4.0 and rebuilt everything. Now the output after applying macdeployqt is slightly different:

    Qt Code: 
    1. @executable_path/../Frameworks/QtWidgets.framework/Versions/5/QtWidgets (compatibility version 5.4.0, current version 5.4.0)
    2. @executable_path/../Frameworks/QtGui.framework/Versions/5/QtGui (compatibility version 5.4.0, current version 5.4.0)
    3. @executable_path/../Frameworks/QtCore.framework/Versions/5/QtCore (compatibility version 5.4.0, current version 5.4.0)
    4. /System/Library/Frameworks/DiskArbitration.framework/Versions/A/DiskArbitration (compatibility version 1.0.0, current version 1.0.0)
    5. /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit (compatibility version 1.0.0, current version 275.0.0)
    6. /System/Library/Frameworks/OpenGL.framework/Versions/A/OpenGL (compatibility version 1.0.0, current version 1.0.0)
    7. /System/Library/Frameworks/AGL.framework/Versions/A/AGL (compatibility version 1.0.0, current version 1.0.0)
    8. /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 56.0.0)
    9. /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 169.3.0)
    To copy to clipboard, switch view to plain text mode 

    Now it's also using @executable_path, but when I start the bundle by double-clicking, the program still cannot call external programs. I tried something I didn't before and ran the bundle from the shell with "open Foo.app" and being started like that, the program can do everything. So, it's definitely the execution enviroment. When I use MuCommander to browse the bundle for the binary, that is hidden inside, and run that, then it also opens a shell window and everything is fine.

    Somehow I have to find out how to spawn a shell execution environment when running a bundle.

    Maybe that article points to the right direction: http://stupidpythonideas.blogspot.de...variables.html

    On OS X, Finder.app is a child of your launchd session, which is a child of the root launchd session, which is process 0. There's no shell anywhere. And when you double-click an app, it asks LaunchServices to run the app. So, your app doesn't inherit anything from Finder, and even if it did, Finder hasn't inherited anything from your login shell.
    He suggests defining an environment in the plist file with the LSEnvironment key. The question is, what has to be there in order to mimick a shell environment. Can be quite a lot I guess.
    Last edited by berliner; 11th December 2014 at 00:52.
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  8. 11th December 2014, 01:20 #8
    jefftee
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    Default Re: Calling external programs via QProcess on Mac OS

    Quote Originally Posted by berliner View Post
    Somehow I have to find out how to spawn a shell execution environment when running a bundle.
    A couple of things I forgot to ask up front (and probably should have):

    1) Have you tried to start the QProcess with the fully qualified path for latex? i.e. /usr/local/bin/latex (or wherever it is installed)

    2) Run otool -L latex to see what external library dependencies latex may have. If unable to load, the start would fail, etc.

    3) I don't have latex installed on my mac, but can you confirm it's a binary executable by running "file latex"? Should show as Mach-O 64-bit executable x86_64. On the off chance that it's a shell script, I believe you have to run the shell scripts by starting the program "sh" or "bash" (or whatever shell you use) and pass latex as the first parameter to the QProcess start (i.e. "sh latex", etc)

    Look forward to your responses, I'm curious to understand why this isn't working because in my usage, I had no problems at all running external processes using QProcess. One difference I do notice is that you seem to be using the start method that takes the program and all arguments as one QString. In my case, use use the overload that takes a QString for the program to start and a QStringList that contains all of the program arguments. I'm using ffmpeg, which takes a lot of arguments, so that's why I chose that overload, but might be worth a try for you to do the same.
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